Such axial bearings are known for instance from hydraulic devices such as pumps, motors or transformers where they are used as bearing between the rotor and the port plate. Other known uses are hydrostatic bearings in a gearbox with helical gears or hydrostatic bearings in other machinery.
In the axial bearing, the pressure difference between both sides of the circular or arc-shaped ridge causes the oil pressure to fall in the adjustable gap when going from the first side to the second side. How the pressure falls and whether a pressure profile from one side of the ridge to the other side of the ridge is linear, progressive or digressive determines the force that this pressure generates to counteract the axial load and with a given axial load determines the gap-height.
For the pressure profile, the shape of the gap is very important. Especially important is whether the walls of the gap, seen in flow direction, are parallel, diverging, or converging. As the gap-height is small, from 2 to 15 microns, minor changes in temperature distribution in the walls of the gap create changes in the diverging or converging of the walls so that the pressure profile in the gap often is unpredictable. The walls of the gap influence the flow in such narrow gaps considerably and the flow theories using laminar or turbulent flow models do not describe the situation properly. As the walls of the adjustable gap move relative to one another, there is a viscous friction. The viscous friction increases with the speed of the relative movement as the gap gets narrower and/or the speed increases and decreases with increasing gap-height. The viscous friction generates heat in the oil that might influence the gap-height due to change in dimensions of the ridge or the bearing surface.
In the known axial bearings, it is very difficult to optimize the axial bearing. A too small axial load leads to a large height of the adjustable gap due to the oil pressure in the adjustable gap between the circular or arc-shaped ridge and the bearing surface. This can lead to a too large oil flow through the gap. This large oil flow will arise if, for average oil viscosity, the average height of the gap is more than 10-20 micron and the pressure of the pressurized hydraulic fluid is more than 10 MPa.
If the axial load is too large, there is too much friction during rotation of the rotor combined with heating of the oil flow due to viscous losses in the adjustable gap. In addition, in an adjustable gap that is very narrow, local deformations or local disturbances in the flow through the gap may occur which might lead to further local heat generation. Local heat generation leads to deformations of the circular of arc-shaped ridge or the bearing surface and to further narrowing of the gap. These deformations might lead to undesired wear as metallic contact between the rotating and stationary parts may occur.